Patent FR-2861165-A1 (FR)
Title: Production of carbon monoxide and/or hydrogen involves cryogenic distillation
Inventor: BRIGLIA ALAIN
IPC: C01B32/40
Filed: 2003-10-20
Abstract: A feed mixture (3) containing at least CO and H 2 is separated (in BF). Either a larger quantity of feed mixture is separated, or a smaller quantity is separated and a recycling gas (6) with a different mixture of CO, H2 and/or methane is returned to the separator. The flow rate and composition of the feed mixture is modified as a function of the flow rate and composition of the recycling gas : The process involves: (i) producing a feed mixture containing at least carbon monoxide and hydrogen in a production device (9); (ii) separating the feed mixture (3) by cryogenic distillation in a separator (BF) with at least one column; (iii) receiving the carbon monoxide (7) and/or hydrogen (8) and/or a mixture of the two; (iv) in one mode of operation, sending a first quantity of feed mixture to be separated in the separator and producing a final product which is carbon monoxide, hydrogen or a mixture of the two; (v) in a second mode of operation sending a second, smaller quantity of feed mixture to be separated in the separator to produce a smaller quantity of final product, and (vi) deriving a recycling gas (6) containing carbon monoxide, hydrogen or methane from the separator with a different composition to the feed mixture and sending the recycling gas to the separator to be separated. The flow rate and composition of the feed mixture is then modified as a function of the flow rate and composition of the recycling gas. In molar fractions, the feed mixture contains up to 10% methane and/or up to 10% nitrogen and/or up to 10% of other impurities, with a minimum of 5% carbon monoxide and 25% hydrogen. The recycling gas is only recycled in the second mode of operation when the need for one of the products (7, 8) drops below a threshold. The composition and/or flow rate of the feed mixture produced by the production device is modified during the second mode of operation, so the carbon monoxide concentration of the second feed gas lowers if the recycling gas is richer in carbon monoxide than the first feed gas and/or increases if the recycling gas is poorer in carbon monoxide than the first feed gas. Similarly, the composition in hydrogen of the second feed gas lowers if the recycling gas is richer in hydrogen than the first feed gas and/or increases if the recycling gas is poorer in hydrogen than the first feed gas. The variation between the feed mixture entering the separator in the first and second modes of operation is not more than 50% of the flow rate, not more than +/- 5% carbon monoxide concentration and not more than +/- 10% hydrogen concentration. The composition and/or flow rate of the feed gas is modified by modifying the operation of the production device. This can be by varying the steam/carbon ratio when the production device is steam methane reformer (SMR) and/or varying the reformer reaction temperature and/or varying the flow of recycled carbon dioxide from a carbon dioxide purifying device (MDEA) to the reformer and/or varying a flow supplying the production device and/or varying the oxygen/carbon ratio feeding the production device when it operates by partial oxidation. An independent claim is made for an installation to carry out the above process, including means of varying the flow rate and/or composition of the feed gas as a function of the flow rate and composition of the recycling gas. There are also means of detecting the flow rate and composition of the recycling gas and means of starting the recycling when the threshold demand for one of the products drops below a threshold and stopping the recycling when demand rises above a threshold. The separator includes a methane scrubbing column and/or a nitrogen scrubbing column and/or a carbon monoxide scrubbing column and/or a depletion column and/or a distillation column.